U.S. Pat. No. 4,574,718 shows such an automatic sewing device, wherein the needle feed movement is always tangentially directed with respect to the seam at the individual position of stitch formation, so that no mentionable forces of displacement between the workpiece and the needle occur. At such a known automatic sewing device there exists the problem that at a rotation of the rotary housing and the hook bearing, the needle bar, the needle jogging drive, and thread take-up lever mechanism and the hook will be altered in their positions relative to each other resulting in stitch length variations. These variations increase proportionally with the angle of rotation per stitch about which the rotary housing and the hook bearing are swivelled. This problem also occurs when, for example, a swivelling of the rotary housing and the hook bearing should be carried out while the needle has come to a standstill within the workpiece, because the needle due to the needle jogging mechanism is exposed to a lateral jogging motion. Due to this problem it is not possible to generate a so-called corner stitch, which may occur as a decorative stitch for example at a shirt collar.
U.S. Pat. No. 2,203,804 shows a two-needle sewing machine, which serves for the production of so-called cork-screw thread seams. At such machines positively and non-avoidably the length of the stitch will be altered at a bent contour of the seam to be produced. The reason for this is the fact that at these sewing machines the swivelling axis of the stitch forming tools does not coincide with the individual axis of the separate needles. For this reason the driving phase between hook and needle alters. Due to this problem in a shaft of a hook swivelling drive there must be interposed a differential gear, which maintains the drive phase of the stitch forming tools to each other. The problems arising at such sewing machines are totally different to the afore-described problems